While putting the top end back on my CB400F, I try to look pretty closely at the parts. That's when I noticed RUST inside of one of the oil tubes that lubes the cam lobes. If rust was there, I wouldn't think that much oil had passed through. But the lobes and rocker looked good. So, I left the tubes off, and kept pushing the kick-starter while watching where the tubes plug into the cylinder head. After a few kicks, I was happy to see oil pump up into the head through both holes.
I still cannot guess how rust formed in there. The restoration continues.
Bob